The present disclosure relates to a fixing device fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
An electrographic image forming apparatus, such as a printer or a copying machine, forms a toner image on a surface of a recording medium, such as a sheet, and then, heats and pressures the recording medium and toner image by a fixing device, thereby fixing the toner image on the recording medium.
As a manner applied in the above-mentioned fixing device, a manner forming a fixing nip heating and pressuring the recording medium and toner image by a fixing roller and a pressuring roller is known. The above-mentioned fixing roller is formed, for example, by covering the outer circumference face of a cored bar made of metal by a resin having high toner releasability. As a heat source heating the above-mentioned fixing roller, for example, a halogen heater is used. The halogen heater is arranged, for example, inside the cored bar of the fixing roller.
On the other hand, another manner (so-called as an “IH (Induction Heating) manner”) using an IH coil as the heat source instead of the halogen heater is known. The above-mentioned IH coil produces magnetic field by conducting electricity. In such an IH manner-type fixing device, instead of forming the fixing nip by the fixing roller and pressuring roller, the fixing nip is often formed by a fixing belt and the pressuring roller. The above-mentioned fixing belt is made of a rotatable endless belt. The magnetic field produced by the above-mentioned IH coil acts on the fixing belt so as to produce eddy current, thereby generating heat in the fixing belt.
As a rotating manner of the fixing belt, a manner rotating the fixing belt together with one or more rollers arranged at an internal diameter side of the fixing belt is known. On the other hand, another manner sliding the fixing belt with respect to a pressuring member arranged at the internal diameter side of the fixing belt is also known.
In the fixing device with such a manner, since temperature rising rate of the fixing belt is high, if the fixing belt is heated in a stopping state, there is a possibility that the temperature of a part of the fixing belt is excessively risen and the excessive risen part receives damage. Then, for example, there is the fixing device including the fixing belt and a rotation detecting part detecting a rotation state of the fixing belt. In this fixing device, in a case where the rotation detecting part does not detect the rotation of the fixing belt for a predetermined time continuously, heating of the fixing belt is suppressed.
In such a fixing device, as a configuration detecting the rotation of the fixing belt, for example, a configuration to attach a detected member co-rotating with the rotation of the fixing belt to an end part of the fixing belt and to detect rotation of the above-mentioned detected member by a rotation detecting part is considered. In a case of applying such a configuration, when the detected member is glued and fixed to the end part of the fixing belt, the detected member may be securely co-rotated with the rotation of the fixing belt. However, if the detected member is glued and fixed to the end part of the fixing belt as mentioned above, the end part of the fixing belt is corrected in a roughly precise round shape by the detected member. Therefore, a shape (an imprecise round shape) of a periphery part of the fixing nip of the fixing belt and the shape (the roughly precise round shape) of the end part of the fixing belt are different from each other, and accordingly, there is a possibility that great stress is added to the fixing belt to break down the fixing belt.
By contrast, when the detected member is not glued to the end part of the fixing belt, the end part of the fixing belt may be deformed in the imprecise round shape in accordance with the shape (the imprecise round shape) of the periphery part of the fixing nip of the fixing belt. Therefore, the stress added to the fixing belt may be reduced and the break of the fixing belt is prevented.
However, if the detected member is not glued to the end part of the fixing belt, there is a possibility that a slip is occurred between the fixing belt and detected member. When the slip is thus occurred, it is impossible to co-rotate the detected member with the rotation of the fixing belt. As a result, there is a possibility that the rotation detecting part cannot detect the rotation of the detected part regardless of the normal rotation of the fixing belt, and then, misdetection indicating abnormality of a rotation state of the fixing belt is caused and the heating of the fixing belt is stopped.
Moreover, in the fixing device using the fixing belt, after the end part of the fixing belt is broken for some reason, a matter of continuously rotating the fixing belt may be caused. With regard to such a point, in the fixing device, the break of the end part of the fixing belt is often detected by a temperature sensor. However, in such a configuration, there is a possibility that the break of the end part of the fixing belt cannot be detected depending on position relationship between an occurrence location of the break and the temperature sensor.